[flang] Don't force SET_EXPONENT(I=...) argument to integer(4)

[klausler]

Summary

The implementation of the folding code for SET_EXPONENT() was written
in such a fashion as to convert the I= actual argument value to a 32-bit
integer. Which is usually not a problem, but it's not always correct
and a test case ran into trouble with it. Fix to allow any kind of
INTEGER without conversion.

[klausler]

Properly handle underflow case in SET_EXPONENT.

flang/include/flang/Evaluate/real.h

public:
 
   static constexpr int DIGITS{binaryPrecision};
   static constexpr int PRECISION{Details::decimalPrecision};
   static constexpr int RANGE{Details::decimalRange};
   static constexpr int MAXEXPONENT{maxExponent - exponentBias};
   static constexpr int MINEXPONENT{2 - exponentBias};
   Real RRSPACING() const;
   Real SPACING() const;
-  Real SET_EXPONENT(int) const;
+  Real SET_EXPONENT(std::int64_t) const;
   Real FRACTION() const;
 
   // SCALE(); also known as IEEE_SCALB and (in IEEE-754 '08) ScaleB.
   template <typename INT>
   ValueWithRealFlags<Real> SCALE(const INT &by,
       Rounding rounding = TargetCharacteristics::defaultRounding) const {
     // Normalize a fraction with just its LSB set and then multiply.
     // (Set the LSB, not the MSB, in case the scale factor needs to
     //  be subnormal.)
     auto adjust{exponentBias + binaryPrecision - 1};
     auto expo{adjust + by.ToInt64()};
+    Real twoPow;
+    RealFlags flags;
+    int rMask{1};
     if (IsZero()) {
       expo = exponentBias; // ignore by, don't overflow
     } else if (by > INT{maxExponent}) {
       expo = maxExponent + binaryPrecision - 1;
-    } else if (by < INT{-adjust}) {
-      expo = -1;
+    } else if (by < INT{-adjust}) { // underflow
+      expo = 0;
+      rMask = 0;
+      flags.set(RealFlag::Underflow);
     }
-    Real twoPow;
-    RealFlags flags{
-        twoPow.Normalize(false, static_cast<int>(expo), Fraction::MASKR(1))};
+    flags |=
+        twoPow.Normalize(false, static_cast<int>(expo), Fraction::MASKR(rMask));
     ValueWithRealFlags<Real> result{Multiply(twoPow, rounding)};
     result.flags |= flags;
     return result;
   }
 
   constexpr Real FlushSubnormalToZero() const {
     if (IsSubnormal()) {
       return Real{};

flang/lib/Evaluate/fold-real.cpp

#endif
                             "SCALE intrinsic folding overflow"_warn_en_US);
                       }
                       return result.value;
                     }));
           },
           byExpr->u);
     }
   } else if (name == "set_exponent") {
-    return FoldElementalIntrinsic<T, T, Int4>(context, std::move(funcRef),
-        ScalarFunc<T, T, Int4>(
-            [&](const Scalar<T> &x, const Scalar<Int4> &i) -> Scalar<T> {
+    if (const auto *iExpr{UnwrapExpr<Expr<SomeInteger>>(args[1])}) {
+      return common::visit(
+          [&](const auto &iVal) {
+            using TY = ResultType<decltype(iVal)>;
+            return FoldElementalIntrinsic<T, T, TY>(context, std::move(funcRef),
+                ScalarFunc<T, T, TY>(
+                    [&](const Scalar<T> &x, const Scalar<TY> &i) -> Scalar<T> {
                       return x.SET_EXPONENT(i.ToInt64());
                     }));
+          },
+          iExpr->u);
+    }
   } else if (name == "sign") {
     return FoldElementalIntrinsic<T, T, T>(
         context, std::move(funcRef), &Scalar<T>::SIGN);
   } else if (name == "spacing") {
     return FoldElementalIntrinsic<T, T>(context, std::move(funcRef),
         ScalarFunc<T, T>(
             [](const Scalar<T> &x) -> Scalar<T> { return x.SPACING(); }));
   } else if (name == "sqrt") {

flang/lib/Evaluate/real.cpp

if (IsNotANumber()) {
     Real result;
     result.Normalize(false, Exponent(), Fraction::MASKR(1));
     return result;
   }
 }
 
 // 16.9.171
 template <typename W, int P>
-Real<W, P> Real<W, P>::SET_EXPONENT(int expo) const {
+Real<W, P> Real<W, P>::SET_EXPONENT(std::int64_t expo) const {
   if (IsNotANumber()) {
     return *this;
   } else if (IsInfinite()) {
     return NotANumber();
   } else if (IsZero()) {
     return *this;
   } else {
-    return SCALE(Integer<32>(expo - UnbiasedExponent() - 1)).value;
+    return SCALE(Integer<64>(expo - UnbiasedExponent() - 1)).value;
   }
 }
 
 // 16.9.171
 template <typename W, int P> Real<W, P> Real<W, P>::FRACTION() const {
   return SET_EXPONENT(0);
 }
 
 template class Real<Integer<16>, 11>;
 template class Real<Integer<16>, 8>;
 template class Real<Integer<32>, 24>;
 template class Real<Integer<64>, 53>;
 template class Real<Integer<80>, 64>;
 template class Real<Integer<128>, 113>;
 } // namespace Fortran::evaluate::value